US2536696A

US2536696A - Primary cell

Info

Publication number: US2536696A
Application number: US631402A
Authority: US
Inventors: Ruben Samuel
Original assignee: Individual
Current assignee: Individual
Priority date: 1945-11-28
Filing date: 1945-11-28
Publication date: 1951-01-02
Anticipated expiration: 1968-01-02

Description

Jan. 2, 1951 s. RUBEN 2,536,696

PRIMARY CELL Filed Nov. 28, 1945 Egg?! f1 -f Z//VC M/ewff//f/M 5 2 iNVENTOR damu/ Fak# HTTORN EY Patented Jan. 2, 1951 UNITED STATES PATENT OFFICE PRIMARY CELL samuel Buben, New Rochelle, N. Y.

Application November 28, 1945, Serial No. 331,402

(Cl. 13B-107) 9 Claims.

This invention relates to electric current producing primary dry cells, more particularly, it relates to sealed dry type alkaline primary cells having a permanganate depolarizer.

Cells of this type which have been described in my copending applications Serial Numbers 575,090, iiled January 29, 1945, 580,172, filed February 28, 1945, now Patent #2,499,419, issued March 7, 1950, 582,594, filed March 14. 1945, and 604,269, filed July 10, 1945, normally develop an internal resistance during the first few hours of their operation substantially higher than that present in the cell when first put into operation. Of these applications. Serial No. 575,090, now Patent No. 2,463,316. discloses and claims a conductive cathode containing an alkali metal permanganate, Serial No. 580,172, now Patent No. 2,499,419, discloses and claims a conductive cathode containing an alkaline earth metal permanganate, Serial No. 582,594, now Patent No. 2,462,998,.discloses and claims a conductive cathode containing a silver or copper permanganate and Serial No. 604,269, nOW Patent N0. 2,422,045,

discloses and claims an alkaline dry cell having an immobilized electrolyte composed of an aqueous solution of an alkali metal hydroxide initially containing a substantial quantity of dissolved zinc.

The object of this invention is to produce an improved alkaline dry cell having a permanga- 'nate depolarizer..

A further object of this invention is to produce an alkaline dry cell having a permanganate depolarizer whose internal resistance can be maintained at substantially the same low level from the period of its initial operation throughout its life. 4

In accordance with this invention these and other objects and advantages which are incidental to its application can be attained by incorporating a small percentage of an electrolyte absorbent material throughout the permanganate cathode.

In the accompanying drawings which illustrate a preferred form of cell embodying features of this invention,

Figure 1 is a sectional view of an alkaline dry cell of the button or ilat type. .f

Figure 2 is a sectional view of a modified struc ture showing a bimetal anode cup.

5 Thealkaline dry cell of this invention includes in general a cathode depolarizer formed of an electronically conductive coherent mass consisting principally of al permanganate compound, a

2 and an anode all enclosed in an airtight container.

In a preferred embodiment of this invention the cathode depolarizer 5 consists of an intimate mixture `of potassium permanganate (KMnO4), graphite and magnesium silicate. While potassium permanganate is preferable, other suitable permanganate compounds include other alkali metal permanganates, such as sodium, lithium, rubidium or caesium, calcium permanganate or other alkaline earth metal permanganates suchv as barium, strontium, zinc and magnesium, silver permanganate, lead permanganate and copper permanganate.

Since these permanganate compounds are low in electronic conductivity, it is normally desirable to mix with them a conductive ingredient in as intimate contact as possible. The preferred ingredient is graphite although other conductive materials such as finely divided silver, conductive cadmium oxide, iron and the like may be used where they do not result in deleterious local reaction.

Where graphite is used micronized natural graphite such as Madagascar, Mexican, Ceylon or Zanzibar graphite has been found to give the best results. It can be used in various proportions, the most useful cathodes containing from one to fifty per cent (l to graphite with live to fifteen percent (5 to 15%) graphite being preferred. The micronized graphite should have an extremely small particle size in the order of five to ten microns diameter. The graphite and finely powdered permanganate compounds are thoroughly mixed to form a graphite coating on the compound particles.

Permanganates in admixture with finely divided conductive materials make excellent depolarizer materials with which it is possible to produce cells which will show a flat voltage discharge curve with continuous output throughout a relatively long period of their life. However, the voltage during this relatively long period will not be as high as that which it is possible to obtain with a cell of this type in the rst few hours of its life. The voltage drop during the initial period of operation is apparently due to the formation of a somewhat impervious brown crust on the cathode surface as a result of reduction of the 0 permanganate. This crust appears to produce a high resistance layer which once formed controls the voltage of the cell.

I have now found that if electrolyte absorbent material is intimately mixed with the permangabarrier member. a spacer and electrolyte carrier u nate graphite mixture conductive `electrolytic One example of a preferred cathode composi- `tion is a mixture of 90 gramsv of potassium permanganate, 10` grams of inicronized Mexican graphite. and grams magnesium silicate.

The' depolarizer isj'preferably made by compressing the nely divided permanganate and the graphite mixtureinto. discs or plates ata pressure of-about 50,000 pounds per square inch. The resultin'product is thencracked and sifted through a screen tol form particles of about 20 mesh A pellet made Vfrom these is converted into a tableta't about2.500` pounds and consolidated into? thecan at about'10.000 pounds per squareinchw `Effective barrier meansislparticularly essential with ,solubledepolarizer of high oxidizing -"value such as thepermanganates. In this case a barrier I ofveryfine porosityand formed of a materiali which is not readily oxidizable by the depolariaer such as av nn'e porosity ceramic layer should be"y used. `l`Ihe barrier prevents direct contact of the solid depolarizer with any oxidizable organic-'spacer used such asl-'paper and also retards dissolvedvdepolarizer from Areaching either the paper or the anode surface. y

Contactof 'oxidizable Vmixture with the solid .or dissolved permanganate depolarizer has two deleteriouseiie'cts namely,

l. Itoxidizes and carbonizesvpaper and 2. It consumesvthe available oxygen in the depolarizer. g f

In order toconipletely prevent circulation of dissolved depolarizer around the edge of4 the barrier. it is desirable that the edge of the barrier vbe cemented or sealed vto the containing wall.

A spacing and electrolyte carrying material lisvrprovlded in the cellto space the electrodes and immobilize theelectrolyte. Most any porous material which is not attacked by the alkali electrolyte. is suited for this purpose. Dexter filter paper and pressed cotton nbre paper though less preferable due to low electrolyte absorption Aare goody examples. However, other suitableporous materials may be used such as 'result in lower cell output efiiciencies.

. 4L Vj that the porous electrolytefcarrierf-may be of such character as-to serve the double function of electrolyte carrier and barrier,A means.

The preferred alkali metarhydroxide elec-v trolyte consists of an aqueous so'lutlon of potassium hydroxide initially-'containing in solution a substantial quantity of. zinc in the form of a compound or compounds commonly called zincatesf y y i The preferred range of concentration of the potassium hydroxide in the electrolyte for a cell of the construction shown in Figure 1 and most other cell structures is from thirty to fifty percent to 50%) KOH." Concentrations above and below these limits .canbe used but generally However, this depends considerablyupon the cell construction andconditions of `use 4and it is feasible with certain structuresv to depart rather widely from the .preferred-"range,v even to thel extent of using such a'high concentration of KOH as to produce anA electrolyte-which is solid vat normal temperatures.. .i "l

For minimum attack onfthe amalgamated zinc anode by the electrolytewhen the cell is standing on open circuit, the v electrolyte should contain all the zinc it will take up at' the temperatures to which the cell isfto `be subjected. Howi ever, I have found lthatproportion's. of zincate nylon nbre',.po1y8tyrene nbre, magnesium Asilicate, magnesium hydroxide, powdered silica Jell or purified'asbestos. When magnesium silicate ls-used, it is made into a Jell by heating a mixture of 20 grams of magnesium silicate and 80 grams of the electrolyte at 80 C. for 4 hours. This Jell is highly conductive, does not separate or flow with'heat and is applied to the anode cup without the use'of any other barrier. For some applications at low current drains, this is the preferred spacer land carrier of the electrolyte as it contains no organic material that can be oxidized.

'Ihe spacing means between the electrodes may thus include, as separate elements both a mintely porous barrier and amore porous elec-- trolyte carrier. vIt is to be understood however,

down to about onehalf this'optlmum concentration will, in many cases, particularly for moderate temperature uses, produce only minute gas generation,;lthe' rate being sunlciently slow to permit generated gastoifgiiffuse` out of tile-cell through the grommet or other sealing means without deleteriously aecting the' desired airtight enclosure of linternal cell elements. 'I'he quantlty of zinc-which will. dissolve n the electrolytes appears to be proportional to the alkali concentration. It"v is preierred thatlthe electrolyte shall contain about frolnl tento twenty grams (10 to 20 gms.) of zinc foreach one hun-'` dred grams (10o` gms.)v of KOH present. The

best'range for 'electrolytes containing thirty to fifty percent (30 to 50%) .KOH is about nfteen to seventeem grams (15 tov 1'? gms.) of zinc per one hundred grams gms.) of KOH.

In the preferredcellsoi the present invention the velectrolyte is neitherconsumed nor evaporated during shelf life and is continuously regenerated during cell operationso that its concentration and volume remains substantially constant. It is therefore necessary to provide only suillcient electrolyte adequately to wet the anode and cathode and 'provide a good conductive path through the spacer.'` In some instances .as little asone cubic centimeter (1 cc.) of electrolyte per ampere-hour rating of the cell can be-used.v l' If the alkaline solution isr not saturated with z'incate, the zinc hydroxide 'formed on the anode ing the desired airtight enclosure, and the life and operation of the cell will not be seriously 76 affected thereby.

Although a potassium hydroxide electrolyte is preferred the present invention contemplates within its scope the possible use of other alkaline metal hydroxide electrolytes such as sodium hydroxide, lithium hydroxide and mixtures of such hydroxides as well as other suitable alkaline electrolytes such as the carbonates of potassium, sodium, lithium, caesium, and rubidium of which the potassium compound is the most desirable in relation to cost and performance.

The anode 2 should have its constituents (other than mercury introduced for amalgamation) formed predominantly. of zinc. It may consist of substantially pure zinc or zinc alloyed with a minor amount of another metal which is capable or being amalgamated and is operable with zinc as anode material Ior example, zinc Witha minor proportion of cadmium.

The zinc anode structure may take on any number of forms, however, it is preferable that they should have a large surface area such as can be obtained with rolled foil or compressed zinc powders. Where zinc is used in the form of powdered anodes, it has been found that a small amount of lead such as four to nve hundredths (.04 to .05%) of 1 percent lead, in the zinc has an inhibiting eieot on gas generation. However,

metals which tend to produce serious local couples with zinc such as iron,V copper and tin should preferably be kept to a low proportion such ,as below two-thousandtnsof one percent (002%) in the anode.

In practice the zinc should beamalgamated before use in the cell to provide an unipotential surface and minimizev the effect of impurity in producing local electric couples which would result in local electrochemical attack.

In Fig. 1 of the drawing illustrating a cell embodying features of this invention, the container I is formed of a sheet of zinc metal I0. The anode 2 which rests upon and makes contact with the zinc is a compressed pellet of amalgamated zinc powder 0.8 gram containing'about .05% lead and about .002% cadmium. Spacer 3 housed in a polystyrene ring 4 is composed of 10 discs of .010l thick Dexter paper, a porous high purity paper, impregnated with an electrolyte solution containing seventyilve grams (75 gms.) of C. P. KOH to 100 milli` liters of water (100 ml.) and twelve (l2 gms.) of zinc oxide. .5 gram of electrolyte is used in the cell. Another preferred type of spacer for the cell is Webril paper (pure cotton libres without a binder) It is normally used in this type of cell in the form of two pieces each 5 mils thick.

The cathode depolarizer 5 consists of a 2 gram compressed pellet made from a mixture contain-` ing 90 grams of potassium permanganate, l0 grams of micronized Mexican graphite and 5 gra-ms of magnesium silicate. This material is housed within steel can top 6 with which it makes contact. A 3 mil thick disc 1 of suitable barrier material is interposed between spacer 3 and anode l and prevents migration of deleterious particles and free circulation of electrolyte. The zinc con-v tainer and the steel can top which serve as terminals of the cell are isolated from each other by neoprene grommet ring 8 of L-shaped crosssection which rests on the container and against which the top is crimped down so as to seal the cell. In the assembly of the cell the paper spacer is compressed about 10% to insure adequate contact.

It is sometimes of advantage to coat the joint between the zinc metal I0, the grommet 8 and the steel cap Il with an inert adhesive of the neoeach 20 mils thick the inner surface of the cup being formed by a, 20 mil zinc layer I0 and the outer surface of the cup being formed by a 20 mil magnesium layer I I. Electrical terminal contact to the outer magnesium layer being obtained by percussion welding of a 5 mil steel strip to the magnesium.

If cell materials of reasonable purity are used there will be substantially no gas generation under normal operating conditions during the life of the cell or at the end of its eiective life. The neoprene grommet 8 will permit sufficient gas diffusion to allow escape of any slight amount of gas which may be generated within the cell due to the local action, if any. If further preventing means are found desirable to provide for unusual conditions they may of course he provided. For example, a more porous neoprene grommet may be used which is impregnated with oil. Another suitable method is to provide the steel can 6 with a l0 mil vent hole in its shoulder at the point l2 which exposes a portion of the" barrier sheet to the atmosphere so that if any excess gas pressure develops it can escape by pushing through the barrier and out through the vent.

While the above description and drawings submitted herewith disclose preferred and practical embodiment of the primary alkaline dry cell of the invention, it will be understood by those skilled in the art that the specic details of construction and arrangement of parts, as shown and described, are by way of illustration and not to be construed as limiting the invention.

What is claimed is:

1. A primary cell comprising a zinc anode, a cathode comprising an electronically conductive coherent mass of a permanganate compound ,in intimate mixture with an electrolyte absorbent hydrogel, a-porous spacer between said anode and said cathode and in contact therewith, and an alkaline electrolyte absorbed in said spacer.'

2. In a primary dry cell a permanganate cathode depolarizer containing magnesium silicate in admixture therewith.

3. A cathode depolarizer for dry alkaline cells comprising an intimate mixture of potassium permanganate, graphite and magnesium` silicate.

4. A cathode depolarizer for dry alkaline cells comprising an intimate mixture of a permanganate, graphite and magnesium oxide.

5. A cathode depolarizer for dry alkaline cells comprising an intimate mixture of a permanganate and powdered glass.

6. A primary cell comprising an amalgamated zinc anode in intimate contact with an electrolyte retaining spacer, a cathode comprising an electronically conductive coherent mass of a permanganate compound in intimate mixture with an electrolyte absorbent material and in surface coherent mass cfa permanganate compounciin` 5 intimate with an electrolyte absorbent material, a'porous spacer between said anode and said cathode and in contact therewith; and an alkaline electrolyte absorbed in said spacer.

8. A primary cellcomprising a zinc anode. a cathode comprising an electronically conductive v coherentv mass of a permanganate compound in intimate mixture with an electrolyte absorbent material, a porous spacer between said anode and' said cathodeand in contact therewith and an yalkalinevelectrolyte absorbed in said spacer, said spacer including a porous barrier of ionically permeable material which is inert to said electrolye and to said permanganate, said porous barrier covering the electroylte-engagin'g surface of said permanganate cathode.

9.` A primarycell comprising a zinc anode, a cathode comprising an electronically conductive coherent masjs vof a permanganate compound in intimate mixturewith an electrolyte absorbent material, an' immobilized body o! alkaline electrov-lyte in contactwithsaid anode and spaced from said cathode, and a porouslbarrier layer of ionically permeable material which is inert to said electrolyte and to said permanganate interposed between and in contact with said cathode and said body of electrolyte,

SAMUEL RUBEN.

REFERENCES crrm The following references are OTHER REFERENCES shou, w. s.. The Battery (is-10), page ss.

of record in thel

Claims

9. A PRIMARY CELL COMPRISING A ZINC ANODE, A CATHODE COMPRISING AN ELECTRONICALLY CONDUCTIVE COHERENT MASS OF A PERMANGANATE COMPOUND IN INTIMATE MIXTURE WITH AN ELECTROLYTE ABSORBENT MATERIAL, AN IMMOBILIZED BODY OF ALKALINE ELECTROLYTE IN CONTACT WITH SAID ANODE AN D SPACED FROM SAID CATHODE, AND A POROUS BARRIER LAYER OF IONICALLY PERMEABLE MATERIAL WHICH IS INERT TO SAID ELECTROLYTE AND TO SAID PERMANGANATE INTERPOSED BETWEEN AND IN CONTACT WITH SAID CATHODE AND SAID BODY OF ELECTROLYTE.